This invention relates to an apparatus for processing tissue samples on slides for a wide variety of purposes. Tissue samples are analyzed for many purposes using a variety of different assays. Pathologists often use histochemistry or immunocytochemistry for analyzing tissue samples, molecular biologists may perform in situ hybridization or in situ polymerase chain reactions on tissue samples, etc. Often the sample to be analyzed will be embedded in paraffin and mounted on a microscope slide.
The assays usually involve the use of antibodies, enzymes and other expensive reagents and it is desirable to keep reagent volume use to a minimum to lower costs. These assays are also quite labor intensive although there are now some automated systems (e.g., the Ventana ESIHC Staining System, the Shandon Lipshaw Cadenza Automated Immunostainer; also see D. J. Brigati et al. Journal of Histotechnology 11:165-183 (1988)). Most automated systems can only perform 40 to 48 slides per run. Fisher automated systems can perform 120 slides per run. Most automated systems which only perform immunocytochemistry do not perform deparaffinizing, histochemistry (such as hematoxylin and eosin staining) and coverslipping steps and these consequently must be done separately by hand which is time and labor intensive. Furthermore, most commercial ready-to-use reagents are not suitable for automated systems which are required to use specially designed reagents. Laboratories which process very large numbers of samples are likely to be willing to pay the large cost associated with buying these automated systems, but small to intermediate sized laboratories find it more cost effective to continue to process samples manually.
A typical immunocytochemistry assay requires a series of many steps. These include: obtaining a tissue sample such as from a biopsy, fixing the tissue in formalin, processing the tissue overnight, embedding the tissue in paraffin, cutting serial sections and mounting on microscope slides and drying. These steps are followed by steps to deparaffinize (treatments in xylene, ethanol and water), and finally the reaction can be performed on the tissue which has been mounted on the slide. Typically a series of solutions including reagents such as antibodies, enzymes, stains, etc. is dropped onto the slide, incubated, and washed off. Finally the sample may be viewed under the microscope.
Clearly there are many individual steps involved and each sample on a slide must be processed individually. Besides being very labor intensive, there are drawbacks associated with the commonly used method of simply dropping solutions on top of the mounted sample on the microscope slide. The solution is not restricted simply to the area of the tissue sample itself and the solution may be relatively deep rather than being a thin film. These features require use of extra reagents which are quite expensive. Leaving the solutions open to the air as they sit on the slide also may lead to evaporation if the samples must incubate for a long period of time. Evaporation leads to concentration or drying out of the reagents and high concentrations may lead to increased background levels which are clearly undesirable. If the solutions evaporate totally the assay will fail. Incubating samples in humidity chambers with covers may prevent evaporation problems, but water droplets which condense onto the humidity chamber cover may fall onto the slides and this will ruin the assay.
Improved methods for more rapidly assaying several samples at once, but without the high cost of automated systems, will be welcomed by small to intermediate sized laboratories. Furthermore, methods which will allow use of smaller amounts of reagents and overcome the drawbacks of processing samples on slides open to the atmosphere will be a welcome advance.